The invention relates to a film-feeding mechanism having at least one transport claw for the intermittent transport of a motion picture film and at least one locking claw to ensure picture steadiness.
The German Patent Application No. DE 40 13 909 A1 discloses a film-feeding mechanism for a motion picture film recording camera having a film guide which has two lateral film guide skids, along which the edge of a motion picture film slides with its film perforations. Located on the optical axis of the motion picture film recording camera is a picture cut-out or picture window which is opened intermittently by opening and closing an iris shutter or a rotating rotary shutter, so that the motion picture film transported intermittently on the film guide is exposed in the region of the picture window.
The claw mechanism of the film-feeding mechanism provided for the film transport has transport claws dipping into the film perforation for the intermittent transport of the motion picture film, and locking claws which, after an intermittent film transport step by the transport claws corresponding to the exposure frequency of the motion picture film, dip into the film perforation with a locking claw tip in order to correct and secure the picture steadiness. During the intermittent transport of the motion picture film, the transport claw tips describe an intrinsically closed crank loop, during which the transport claw tips initially dip into the film perforation, then carry out the film transport step, slip out of the film perforation again and return into their initial position. At the reversal points of the crank loop of the transport claws, the locking claw tips, describing an oscillatory movement, dip into the film perforation at high speed, perform a possible correction of the alignment of the motion picture film in the plane of the film and secure the picture steadiness of the motion picture film during the exposure of a film picture. Following the exposure of a film picture of the motion picture film, they are drawn out again, so that the motion picture film is released for a further film transport step.
Both the dipping of the transport claw tips and locking claw tips and the transfer from the transport claw tips to the locking claw tips and vice versa require, in addition to exact coordination of the kinematics of the transport claws and locking claws, exact alignment with the film perforation if undesired noise occurs as a result of transport and locking claw tips not dipping exactly into the film perforation or as a result of a lack of time coordination of the movement of the transport and locking claws. Furthermore, it is also possible for damage to occur to the film perforation or to the surface of the motion picture film.
For the exact alignment of the transport and locking claw tips with the film perforation and for the correct transfer from the transport claw tips to the locking claw tips, the knowledge of the dimensions of the motion picture film and its tolerances is imperative. For instance, in the case of a 35 mm unexposed film to DIN 15502, the width of the unexposed film is 34.97 mm with a tolerance of ±0.03 mm, the pitch between two successive perforation holes is 4.74 mm with a tolerance of ±0.01 mm, and the spacing of the outer edge of the perforation holes from the lateral edge of the motion picture film is 2 mm with a tolerance of ±0.07 mm. Although these film tolerances do not occur within a reel of unexposed film, they certainly occur from reel of film to reel of film, depending on the production batch or the unexposed film type or type of use, such as “indoor film”, “daylight film” or the like.
To minimize noise, it is known to optimize the transfer from the locking claws to the transport claws in such a way that, by a stepwise claw adjustment or “pitch adjustment”, a flexible lifting adjustment and transfer adapted to the motion picture film is carried out from the locking claws to the transport claws. This pitch adjustment ensures noise-optimized film transport, since the transport claws themselves, even in the case of a shrunken motion picture film, can stick in exactly, transport and stick out on their optimum claw curve. Because of the tolerances mentioned above, for example in the case of a motion picture film that has shrunk by 0.01 mm per perforation spacing, the insertion of the transport claw tips has to be adjusted by 0.02 mm and, at the same time, the stroke of the transport claws also has to be reduced by 0.05 mm, for example. This adjustment is made on an operating element connected to the lifting eccentric of the film transport mechanism, known as a “pinch adjust”, which converts the vertical adjustment into an approximately horizontal displacement of the lifting eccentric in the 1/100 mm range.
Despite this known measure of pitch adjustment, disruptive noises and damage to the film perforation or to the surface of the motion picture film continue to occur during film transport, which are intended to be avoided or minimized by the present invention.